Fan impeller and heat dissipating device having the same

ABSTRACT

A heat dissipation device includes an electric fan having a fan impeller with a hub and a heat sink. A plurality of main blades and subsidiary blades extend radially and outwardly from the hub and alternate with each other. The electric fan forms an air inlet and an air outlet. The main blades have connecting portions on the hub which are extended towards a center of the hub at the air outlet. The subsidiary blades have a smaller radial length than the main blades. The subsidiary blades each have a connecting edge on the hub which is extended toward the center of the hub adjacent to the air outlet. The fan impeller drives more air to the center of the air outlet, whereby more air can flow to a center of the heat sink.

CROSS-REFERENCE TO RELATED APPLICATION

Relevant subject matter is disclosed in co-pending U.S. patent application Ser. No. 12/325,281 filed on Dec. 1, 2008 and entitled “FAN IMPELLER AND HEAT DISSIPATING DEVICE INCORPORATING THE SAME”. The co-pending U.S. patent application is assigned to the same assignee as the instant application. The disclosure of the above-identified co-pending application is incorporated herein by reference.

BACKGROUND

1. Technical Field

The disclosure relates to a heat dissipating device, and particularly to an electric fan having an improved fan impeller and a heat dissipation device having such a fan impeller.

2. Description of Related Art

With continuing development of electronic technology, a heat-generating electric component such as CPU (central processing unit) is generating more and more heat which requires immediate dissipation. Generally, a heat sink is thermally attached to the CPU, and an electric fan is mounted on the heat sink for providing an airflow to cool the CPU.

A typical electric fan includes a fan impeller having a cylindrical-shaped sidewall and a plurality of blades extending radially from the sidewall of the fan impeller. A bottom wall of the fan impeller facing the heat sink is flat and is perpendicular to the sidewall. When the blades rotate to generate an airflow flowing to the heat sink, the bottom wall of the fan impeller prevents the airflow from flowing to a center of the heat sink just under the fan impeller of the electric fan. FIG. 6 shows a flow field 92 of the airflow produced by a typical electric fan simulated by a computational fluid dynamics (CFD) software. The flow field 92 includes a central dark region through which almost no air flows and a surrounding bright region through which a strong air flows. It is found that most of the airflow flows out from a circumference of the impeller and an amount of the airflow at the center of the heat sink is approximately zero. However, the center of the heat sink is usually attached to the heat-generating electric component and has more heat than other portion of the heat sink. Thus, the airflow provided by the typical electric fan cannot efficiently dissipate heat of the heat sink absorbed from the heat-generating electric component.

Therefore, a heat dissipation device having an improved fan impeller is desired to overcome the above describe shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric, exploded view of a heat dissipating device, according to a first embodiment.

FIG. 2 is an isometric view of a fan impeller of the heat dissipating device of FIG. 1.

FIG. 3 is a plan view of the fan impeller of FIG. 2.

FIG. 4 is an isometric view of the fan impeller of FIG. 2, but viewed from another aspect.

FIG. 5 is a view of an airflow field of the fan impeller of FIG. 2 simulated by a computational fluid dynamics software.

FIG. 6 is a view of an airflow field of a prior fan impeller simulated by a computational fluid dynamics software.

DETAILED DESCRIPTION OF THE EMBODIMENT

Referring to FIG. 1, a heat dissipating device 10 according to a first embodiment is shown. The heat dissipating device 10 is assembled to a heat source (not shown), such as a CPU, for dissipating heat of the heat source. The heat dissipating device 10 includes a heat sink 4, an electric fan 1, two fixing members 7 for fixing the electric fan 1 onto the heat sink 4, and two heat pipes 8. The electric fan 1 is mounted on the heat sink 4 and generates an airflow flowing through the heat sink 4 to take away heat from the heat sink 4.

The heat sink 4 includes a base plate 6 and a heat dissipating body 5 located on the base plate 6. The base plate 6 defines two first receiving grooves 61 in an upper surface 62 thereof. The two first receiving grooves 61 are semi-circular. A bottom surface 63 of the base plate 6 is used for thermally contacting with a heat source such as a CPU for absorbing heat therefrom. The heat dissipating body 5 includes a plurality of parallel fins 51 spaced from each other. Two adjacent fins 51 define an airflow channel therebetween. Two second receiving grooves 55 are defined at a bottom portion 54 of the heat dissipating body 5 corresponding to the two first receiving grooves 61, respectively. The two second receiving grooves 55 are semi-circular. Each first receiving groove 61 and a corresponding second receiving groove 55 cooperatively define a circular receiving channel. The heat dissipating body 5 defines an elongated groove 53 through a middle of a top portion 56 thereof. The groove 53 is perpendicular to each of the fins 51. Two holes 52 are defined in the heat dissipating body 5 and symmetrically located at two opposite sides of the groove 53. Each heat pipe 8 is U-shaped and includes a condenser section 81 and an evaporator section 82. The condenser section 81 of each heat pipe 8 is received in one of the two holes 52. The evaporator section 82 of each heat pipe 8 is received in one of the two receiving channels. The two fixing members 7 are symmetrically mounted on a top of the heat dissipating body 5. The electric fan 1 is fixed onto the fixing members 7 by screws (not shown).

Referring also to FIGS. 2-4, the electric fan 1 includes a fan bracket 2 and a fan impeller 3 received in the fan bracket 2. The fan impeller 3 includes a hub 31, a plurality of main blades 32 and subsidiary air-guiding blades 33 extending radially and outwardly from an outer circumferential surface of the hub 31. The hub 31 is bowl-shaped and includes a bottom wall 317 and a sidewall 314 extending upwardly and outwardly from the bottom wall 317. An air inlet 311 is formed at a top side of the fan bracket 2 and an air outlet 312 is formed at a bottom side of the fan bracket 2. The air outlet 312 is provided adjacent to and faces the heat sink 4. The bottom wall 317 of the hub 31 is located at the air outlet 312. The sidewall 314 tapers from the air inlet 311 towards the air outlet 312. Accordingly, an outer diameter of the hub 31 gradually decreases along an axial direction from the air inlet 311 towards the air outlet 312. The hub 31 defines a receiving space 313 adjacent to the air inlet 311. An inner surface 315 of the hub 31 surrounds the receiving space 311. A diameter of the receiving space 313 defined by the inner surface 315 decreases along the axial direction from the air inlet 311 towards the air outlet 312. Each main blade 32 has a connecting side edge 34 on the sidewall 314, and the connecting side edge 34 is extended from the sidewall 314 of the hub 31 at the air inlet 311 towards a center of the hub 31 at the air outlet 312. Each subsidiary air-guiding blades 33 is located between two adjacent main blades 32. Each subsidiary air-guiding blades 33 has a much smaller radial length (i.e., height) than each main blade 32. A radial length of the subsidiary air-guiding blades 33 decreases along the axial direction from the air inlet 311 towards the air outlet 312. The subsidiary air-guiding blades 33 has a connecting side edge 35 on the sidewall 314, and the connecting side edge 35 is extended from the sidewall 314 of the hub 31 towards a center of the hub 31 at the air outlet 312. The connecting side edge 34 of the main blade 32 has a greater axial length than the connecting side edge 35 of the subsidiary air-guiding blades 33. The main blade 32 has a much greater radial length than the subsidiary air-guiding blades 33. The main blades 32 and the air-guiding blades 33 cooperatively drive the airflow to a center of the hub 31 at the air outlet 312 when the fan impeller 3 is rotated.

FIG. 5 shows a flow field 91 of the airflow produced by the fan impeller 3 simulated by a computational fluid dynamics software. The flow field 91 includes a central dark region through which almost no air flows and a surrounding bright region through which a strong air flows. The dark region of the flow field 91 is smaller and more uniform than the dark region of the flow field 92 generated by the conventional fan impeller of FIG. 6. When the fan impeller 3 rotates, the airflow flows from the air inlet 311 towards the heat sink 4. Due to the diameter of the outer circumference of the hub 31 decreasing along a direction from the air inlet 311 towards the air outlet 312, more airflow can flow to the center of the air outlet 312. In addition, the main blades 32 and the air-guiding blades 33 can drive more air of the airflow to flow to the center of the air outlet 312. Therefore, an amount of the air of the airflow driven by the fan impeller 3 to the center of the heat sink 4 is increased. The hub 31 occupies a smaller space than a conventional hub. Thus the main blades 32 can have a relatively larger size. Accordingly, the amount of airflow generated by the main blades 32 is increased in comparison with the prior art.

It will be obvious that, within the scope of the invention, many variations are possible to those skilled in the art. The scope of protection of the invention is not limited to the example given herein. 

1. A fan impeller for generating airflow, comprising: a hub forming an air inlet and an air outlet at two opposite sides thereof, the hub having a diameter gradually decreasing along an axial direction from the air inlet towards the air outlet; a plurality of main blades extending radially and outwardly from an outer circumferential surface of the hub, the main blades each having a connecting edge on the hub, the connecting edge of each main blade extending towards a center of the hub at the air outlet; and a plurality of subsidiary blades extending radially and outwardly from the outer circumferential surface of the hub, the main blades and the subsidiary blades being alternately arranged around the hub, each of the subsidiary blades having a smaller radial length than each of the main blades, each of the subsidiary blades having a connecting edge on the hub, the connecting edge of the each subsidiary blade extending towards the center of the hub at the air outlet, the main blades and the subsidiary blades cooperatively driving the airflow to a center of the air outlet when the impeller is rotated.
 2. The fan impeller as claimed in claim 1, wherein the main blade has a greater axial length than the subsidiary blade.
 3. The fan impeller as claimed in claim 1, wherein a radial length of each of the subsidiary blades decreases along an axial direction from the air inlet towards the air outlet.
 4. The fan impeller as claimed in claim 1, wherein the hub defines a receiving space adjacent to the air inlet.
 5. The fan impeller as claimed in claim 4, wherein the hub is bowl-shaped, the hub forms an inner surface surrounding the receiving space, and a diameter of the receiving space defined by the inner surface decreases along an axial direction from the air inlet towards the air outlet.
 6. A heat dissipating device comprising: a heat sink comprising a plurality of heat dissipating fins; and an electric fan mounted on the heat sink for generating airflow flowing through the fins of the heat sink to take away heat from the heat sink, the electric fan comprising: a hub forming an air inlet and an air outlet, the air outlet being located between the air inlet and the heat sink, the hub having a diameter gradually decreasing along an axial direction from the air inlet towards the air outlet; a plurality of main blades extending radially and outwardly from an outer circumferential surface of the hub, the main blades each having a connecting edge on the hub, the connecting edge of each main blade extending towards a center of the hub at the air outlet; and a plurality of subsidiary blades extending radially and outwardly from the outer circumferential surface of the hub, the blades and the subsidiary blades being alternately arranged around the hub, the subsidiary blades each having a smaller radial length than each of the main blades, the subsidiary blades each having a connecting edge on the hub, the connecting edge of the each subsidiary blade extending towards the center of the hub at the air outlet, the main blades and the subsidiary blades driving the airflow to a center of the air outlet when the impeller is rotated.
 7. The heat dissipating device as claimed in claim 6, wherein each of the main blades has a greater axial length than each of the subsidiary blades.
 8. The heat dissipating device as claimed in claim 6, wherein a radial length of each of the subsidiary blades decreases along an axial direction from the air inlet towards the air outlet.
 9. The heat dissipating device as claimed in claim 6, wherein an end of the hub defines a receiving space adjacent to the air inlet.
 10. The heat dissipating device as claimed in claim 9, wherein the hub is bowl-shaped, and the hub forms an inner surface surrounding the receiving space, and a diameter of the receiving space defined by the inner surface decreases along an axial direction from the air inlet towards the air outlet. 